Surgical needles are used in different medical procedures, for example for taking specimens or for injecting substances. The use of a cannula and a stylet (or stylus or mandrin) contained therein as electrodes for measuring bioimpedance is known from the U.S. Pat. No. 6,337,994 B1.
In an arrangement for measuring bioimpedance shown in the drawings of the U.S. Pat. No. 6,337,994 in FIG. 7, the electrical coupling of a needle electrode, formed by the cannula, and a stylet electrode of the stylet, moveable within the cannula, to an impedance meter is implemented by means of alligator clip connectors to be attached to the needle electrode and to the stylet electrode, which does not necessarily enable a reliable electrical coupling of the electrodes to the impedance meter when measuring bioimpedance, for example when preparing a medical procedure. After measuring the bioimpedance, the line leading from the cannula to the impedance meter may hinder the work when the cannula is meant to be used for taking specimens or for injecting a substance. In this case, it is possible to disconnect the line, however, disconnecting the alligator clip connectors from the cannula is laborious and increases the risk involved in the procedure to be carried out using the cannula. This is, among other things, due to the fact that when removing the alligator clip connectors, the cannula may tend to shift from its defined position.
The applicant's Finnish patent 123246 describes an arrangement for measuring bioimpedance, whereby only the electrodes of the electrode pattern contained in the stylet are used for measuring bioimpedance. The wiring for measuring bioimpedance can be easily removed by means of the measurement arrangement used in the patent 123246 because the cannula is not used as an electrode. However, the measurement arrangement presented in the patent is not fit for use in a situation in which the cannula must be used as the other measuring electrode or as one of the measuring electrodes.